The printed wiring boards widely used in the electronics and other fields may often be produced by any of the additive methods using electroless plating. The additive methods are roughly classified into full-additive methods in which wiring is formed by only electroless plating and semi-additive methods in which wiring is formed by electroless plating and subsequent electroplating. More specifically, the surface of a substrate is roughened and then provided with a catalyst, followed by electroless plating such as electroless copper plating (the steps so far are called as a full-additive method), and if necessary, subsequent electroplating such as electrolytic copper plating (the steps so far are called as a semi-additive method), thereby forming a printed wiring board.
As described above, before electroless plating, a catalyst is used in order to activate a substrate. A reason for the use is that the substrate, which is served as an underlying member, is not electroconductive, and thus by previously carrying (imparting) of catalyst on the substrate, a plating film made of such as copper is easily formed on the substrate. The catalyst includes noble metals such as Pd, Ag, Au or Pt. In order to promote imparting effect of the catalyst to the underlying member, generally, a silane coupling agent is widely used (for example, Patent Documents 1 and 2).
The silane coupling agent is generally an organic silicon compound represented by Y—(CH3)n—Si—(OR)3-n. In this formula, “Y” is an organic functional group such as an amino, epoxy, methacrylic, vinyl or mercapto group; and “OR” is a hydrolyzable group such as OCH3, OC2H5, or OCOCH3. The silane coupling agent has, in a single molecule thereof, both of the organic functional group “Y”, which relates to a reaction or an interaction with an organic substance, and the hydrolyzable group “OR”. Thus, the silane coupling agent has an effect of being bonded to, e.g., an organic polymer through “Y”, and further forming a chemical bond to an inorganic substance surface by the hydrolysis and reaction of “OR” so that the two substances, which are different in chemical properties from each other, are strongly bonded to each other. When, e.g., Pd is used as the catalyst, it can be considered that particles of Pd is easily bonded to “OR” because of a high hydrophilicity and activity of “OR” so that Pd is coordinate-bonded to “OR” to form a chelate. Thus, the silane coupling agent comes to exist in the state of being bonded to both of the surface of an oxide (material to be plated) and the Pd particles. It is therefore considered that by electroless plating performed after the imparting process of the catalyst such as Pd, the resultant plating film adheres strongly to the surface of the oxide (material to be plated) through the silane coupling agent so that the adhesive strength therebetween is heightened. In the meantime, when the “Y” has an amino group, the whole of the silane coupling agent becomes hydrophobic so that the agent is affinitive with a photoresist painted onto a substrate made of, e.g., glass to be easily bonded to the substrate. As a result, the photoresist adheres strongly to the substrate through the silane coupling agent, and further the presence of the silane coupling agent also on the surface of the photoresist makes the following good: the adhesiveness of a plating film onto the surface of the photoresist.